555-Timer Circuit
Electrical Engineering
Author: Dr. Farid Farahmand
Date Created: October 27, 2012
Subject: Engineering
Schedule: 150 minutes
References:
Learn about 555-Timer Chip: http://en.wikipedia.org/wiki/555_timer_IC
Circuits you can build using 555-timer ship: http://www.555-timer-circuits.com/
YOUR NAMES
CLASS
DATE
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555-Timer Circuit
Electrical Engineering
Consider the following timer circuit operating in astable mode:
Figure 1. 555-timer circuit in astable mode
The frequency of the output signal can be calculated using the following formula:
Note that
Assume C1 on the schematic is the same value as C.
1- Use the online programmable calculator to find the following values:
a. Period:
___________________________
b. High-time: ___________________________
c. Low-time: ___________________________
You can program the calculator as shown below. Once you enter the formula click on “=” sign in the
bar:
2- Open the circuit simulator (www.circuitlab.com ) and place a 555-timer chip as shown
below. Add pin numbers to the 555-timer chip as shown:
3- Build the circuit shown in Figure 1, above, using the Circuit Lab simulator. Take a snapshot
of your circuit. You must have your name depicted on the circuit.
4- Use the Timer Domain analysis to measure the output frequency. Take a snapshot of the
output signal.
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5- Using the obtained results from the simulator measure the output period, high-time, and
low-time.
a. Period:
___________________________
b. High-time: ___________________________
c. Low-time: ___________________________
d. Vpp: _______________________________
e. Voffset:
___________________________
6- Using the provided Proto-board sheet (ask your instructor for one), draw all the
connections in order to build the circuit shown in Figure 1. Note that 555 chip looks like
this:
Figure 2. Chip schematic
7- When you finished drawing the wires on the Proto-board sheet, check everything again!
8- Did you check it again?
a. We certify that both of us checked the circuit (Your Initials): _____________________
9- Create a list-of-material for your circuit (what components you need for your circuit). Once
you have this list, present it along with your Proto-board sheet to the instructor.
Reference Designator
Value (unit)
Measured/Checked Quantity
Figure 3. List of materials
10- Check/measure the value of the resistors, capacitors, etc. and make sure they are correct.
Check/record these values in the table above. Note the value of the capacitor. If the
capacitors have polarity make sure you connect them properly (NEGATIVE leg must be
connected to the GROUND).
Go to the NEXT page 
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11- Watch this video to learn how to build your signal generator circuit (how do you like the
music? )
12- Complete building the circuit on the Prototype board.
13- Test the circuit using the scope. Take a snapshot of at least one complete cycle of the output
(pin 3 of the 555-timer chip).
14- Using the oscilloscope measure the following:
a. Period:
___________________________
b. High-time: ___________________________
c. Low-time: ___________________________
d. Vpp: _______________________________
e. Voffset:
___________________________
15- Show to the instructor that the LED is working properly. Make sure you receive an approval
code from the instructor:
a. Approval Code:
___________________________ (unique code for each team)
16- What happens if you connect the output signal to a speaker instead of a LED? What do you
hear? Why? Explain.
17- Use Excel to plot the period of the circuit shown in Figure 1 as a function of frequency.
Assume R1 and R2 are the same values shown in Figure 1. Assume the value of C is changing
as follow: 10 nF, 100nF, 1000nF, 10,000nF, 100uF, 1000uF. You must use a Bar-Graph. Show
your plot below. Note that your plot must have the following: X-axis label, Y-axis label, Title,
and Legend. You must also have a note on the plot showing your names.
 Extra Credit: Consider building any of the following circuits for extra credit (must be done
individually): http://www.555-timer-circuits.com/
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